倒伞曝气机内部流动分析及曝气性能研究

发布时间：2018-06-19 08:41

本文选题：倒伞曝气机 + 液面捕捉　；参考：《江苏大学》2017年硕士论文

【摘要】：本文的研究是在国家重点研发计划(2016YFB0200901)的资助下开展的。倒伞曝气机广泛应用于污水处理工艺中,具有结构简单、作用面积大和动力效率高等优点。其流动涉及水跃、卷吸和波破碎等复杂流动,同时其曝气性能受叶轮转速、叶轮浸没深度、叶片数等参数的影响较大,使得在内流分析和曝气性能预测等方面存在很多亟待解决的难题。为了揭示倒伞曝气机流动机理并建立倒伞曝气机曝气性能预测方法,本文采用理论分析、试验测试和数值模拟相结合的方式对倒伞曝气机的运行特性和曝气性能进行深入研究。主要工作和研究成果如下:1.在搭建倒伞曝气机高速摄影试验台的基础上,对倒伞曝气机驱动的曝气池流动情况进行了研究。研究发现:(1)水跃扬起的液体主要来源于辐板上侧,液体从辐板上侧前一个流道滑移到下一个流道后经叶片工作面抛射而出。(2)叶轮旋转时会在叶片背面形成低压区,并卷吸大量空气,空气起始于辐板下侧叶片背面,紧贴辐板呈三角形分布。2.结合高速摄影试验,采用VOF法(Volume of Fluid Method)对倒伞曝气机进行三维非定常数值模拟。结果表明:(1)液面波动最先出现在叶轮附近,随后向壁面传播直至液面出现整体波动,自由液面速度由中心逐渐向壁面增大。中截面环流漩涡的变化与液面波动相一致。(2)倒伞曝气机对浅层液体的搅动作用明显强于底层液体,湍动能也比较大;深水区流体主要由倒伞曝气机的提升力带动,该层流体流动平缓湍动能低。3.开展了倒伞曝气机曝气性能试验,研究了不同转速、液位高度、叶片数、浸没深度等参数对曝气性能的影响。结果表明:(1)在曝气池液位高度不变、叶轮与液面持平的情况下,标准氧总转移系数和标准充氧能力与转速成正比,而标准动力效率与转速没有明确的关系。(2)浸没深度对倒伞曝气机曝气性能的影响与转速的大小有关,在低转速时,浸没深度对标准氧总转移系数、标准充氧能力和标准动力效率的影响较小;在高转速时,标准氧总转移系数、标准充氧能力和标准动力效率随着深度的增加而增强。(3)转速保持恒定时,倒伞曝气机的标准氧总转移系数随着液位高度的增加而降低,标准充氧能力和标准动力效率的变化趋势则相反。(4)叶片数对倒伞曝气机曝气性能影响较小。4.基于量纲分析法建立了倒伞曝气机曝气性能预测模型,解决了缩比样机无法预测原模型曝气性能的问题。结果表明:(1)倒伞曝气机的改进吸收数和动力效率数仅与弗劳德数有关。(2)大尺寸倒伞曝气机标准充氧能力和标准动力效率的预测值与实测值相差不大,标准充氧能力的最大相对预测误差为2.56%,平均相对误差为1.39%;标准动力效率的最大相对预测误差为6.14%,平均相对误差为4.05%。表明本文所建立的曝气性能预测模型精度较高。
[Abstract]:The research in this paper is supported by the National key R & D Program (2016YFB 0200901). The inverted umbrella aerator is widely used in wastewater treatment process, which has the advantages of simple structure, large action area and high power efficiency. Its flow involves complicated flow such as hydraulic jump, entrainment and wave breakage, and its aeration performance is greatly affected by impeller speed, impeller immersion depth, blade number, etc. Therefore, there are many problems to be solved in the aspects of flow analysis and aeration performance prediction. In order to reveal the flow mechanism of the inverted umbrella aerator and to establish a prediction method for the aeration performance of the inverted umbrella aerator, the operational characteristics and aeration performance of the inverted umbrella aerator were studied in this paper by the combination of theoretical analysis, test and numerical simulation. The main work and research results are as follows: 1. On the basis of setting up the high-speed photography test bench of the inverted umbrella aerator, the flow of the aeration tank driven by the inverted umbrella aerator was studied. It is found that the liquid raised by the water jump mainly comes from the upper side of the spoke plate. When the liquid slips from the front channel of the upper side of the spoke board to the next channel and ejects from the blade face through the blade face, the impeller rotates and forms a low pressure area on the back of the blade. The air begins at the back of the blade at the lower side of the radiate plate, and is closely attached to the radiate plate as a triangle distribution. 2. Combined with high-speed photography test, the three-dimensional unsteady numerical simulation of the inverted umbrella aerator was carried out by using VOF volume of fluid method. The results show that the liquid level fluctuation first occurs near the impeller, then propagates to the wall until the whole wave occurs, and the free surface velocity increases gradually from the center to the wall. The variation of the swirl in the middle section is consistent with the liquid level fluctuation. (2) the stirring effect of the inverted umbrella aerator on the shallow liquid is obviously stronger than that of the bottom liquid, and the turbulent kinetic energy is also relatively large, and the fluid in the deep water area is mainly driven by the lifting force of the inverted umbrella aerator. The flat turbulent kinetic energy of the fluid flow in this layer is low. The aeration performance test of inverted umbrella aerator was carried out, and the effects of different rotational speed, liquid level height, blade number and immersion depth on aeration performance were studied. The results show that the total standard oxygen transfer coefficient and the standard oxygenation capacity are in direct proportion to the rotational speed under the condition that the liquid level of the aeration tank is constant and the impeller is equal to the liquid level, and the total standard oxygen transfer coefficient and the standard oxygenation capacity are in direct proportion to the rotational speed. However, the influence of immersion depth on aeration performance of inverted umbrella aerator is related to the speed of aeration. At low speed, the depth of immersion affects the total transfer coefficient of standard oxygen. At high speed, the total transfer coefficient of standard oxygen, the standard oxygenation capacity and the standard dynamic efficiency increase with the increase of depth. The total standard oxygen transfer coefficient of the inverted parachute aerator decreases with the increase of liquid level height, but the change trend of standard oxygenation capacity and standard dynamic efficiency is opposite. 4) the number of blades has little effect on aeration performance of the inverted umbrella aerator. Based on dimensional analysis, the aeration performance prediction model of inverted parachute aerator is established, which solves the problem that the prototype can not predict the aeration performance of the original model. The results show that the improved absorption and dynamic efficiency of the inverted parachute aerator are only related to the Froude number. 2) the predicted values of the standard oxygenation capacity and the standard dynamic efficiency of the large size parachute aerators are not different from the measured values. The maximum relative prediction error of the standard oxygenation capacity is 2.56, the average relative error is 1.39, the maximum relative prediction error of the standard dynamic efficiency is 6.14 and the average relative error is 4.05. It shows that the prediction model of aeration performance established in this paper has high accuracy.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X703

【参考文献】